Wednesday, March 1, 2017

What was space like before the big bang?

If the universe began with the big bang, there was no space-time before it—and no such thing as "before." However, it may be possible that our universe bubbled off a higher-dimensional "multiverse," where new universes pop into existence all the time.

Some people think that every black hole leads to a new universe, and that our big bang began as a singularity from a black hole in another universe. Others speculate that higher-dimensional spaces called branes (short for "membranes") can collide, sparking big bangs like ours. Astronomers have made a number of observations about the cosmos that line up nicely with what a universe born from a big bang would be like. They include:

Galaxies are flying away from each other. While many galaxies have different motions through the cosmos (some orbit each other in clusters and groups, for instance), as a whole they are generally flying apart. That means the universe is expanding and the expansion must have started sometime in the distant past.

We can watch galaxies develop and evolve the farther we look. Because of the finite speed of light, the deeper we look into space, the farther back we peer into time. Looking back over many billions of years, we can see galaxies form and evolve. That implies that the universe has a finite start date. 

The big bang set the quantities of different types of elements. A few minutes after the big bang, the universe was essentially a nuclear furnace, produc-ing the precise amounts of deuterium, lithium, and helium we see in interstellar matter today.

The "cosmic microwave background" is all around us. As the universe cooled sufficiently for atoms to form, light was able to pass by matter more easily.

That light, which itself has cooled as the universe expanded, is called the cosmic microwave background (CMB) and has the exact properties one would expect from a universe that began with a bang. The CMB was discovered serendipitously by two radio astronomers, Arno Penzias and Robert Wilson, in 1965.

The fact is, we will never be able to "see" beyond the cosmic microwave back-ground. Prior to its formation—some 290,000 years after the big bang—light was scattered in a thick soup of sub-atomic particles. The CMB remains an impenetrable fog that we cannot probe with light, making an actual glimpse of the pre-CMB past forever elusive.

From National Geographic's "Are We Alone?" special magazine:

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